Emulsion sensitometry



March 1952 E. A. WILLIFORD EkAL 2,

' EMULSION SENSITOMETRY Filed Oct. 14, 1948 2 SHEETSSHEET l Shortstop(Fixing) Sol n.

INVENTORS Edward Allan Williford Monroe H. Sweet ATTORNEYS March 1952 E.A. WILLIFORD ETAL EMULSION SENSITOMETRY A Filed Oct. 14, 1948 2SI-lEETS-SHEET 2 3 0- 75,95,||5 min. 35 min. .l5 min.

5min. Ripening Test Liquid Sensitometry o i g 2.0 m n.

"a I O |.o- Fig. 3. Y-

Log Relative Exposu're 95min. (Sm in. 35min. "2.5 H5 min. Ripening TestI Conventional (Dry) 2.0- Sensitometry [5mina I: 5min. g 0min. E

Fug. 4. '.5--

| I I l l 9.5 0.0 0.5 L0 L5 2.0 2.5

l E Log Re uhve xposure INVENTORS Edward Allan Williford Monroe H. SweetATTORNEYS Patented Mar. 25, 1952 EMULSION SENSITOMETRY Edward AllanWillifordand Monroe H. Sweet,

Binghamton, N. Y., assignors to General Aniline & Film Corporation, NewYork, N. Y., a

corporation of Delaware Application October 14,1948, Serial No. 54,448

Claims.

This invention relates to an improved method for controlling andmeasuring the comparative light sensitivity and contrast characteristicsof photographic emulsions, and for other measurements involvingdetermination of densities produced on development of photographicemulsion coatings.

Photographic films and papers are ordinarily prepared by coating asuitable base, such as film, paper or other fabric, with a photographicemulsion, particularly of the type containing a light-sensitive silverhalide suspended in gelatin or other viscous protective colloid, andallowing the coating to dry on the base. The emulsion is generallyprepared in batches, and since the photographic characteristics of theresulting coatings are sensitive to numerous variables in the course ofmanufacture, it is customary to test each batch before applying it to abase, e. g., in order to insure that uniform quality will be maintained.Heretofore, the testing method employed approximated the intended use ofthe emulsion. Thus in carrying out the test, a sample of the emulsionwas coated on a sheet of backing material, and dried thereon. Theresulting sensitized material was cut into strips, exposed to light ofgraduated intensity, developed, washed and dried, and then subjected tomeasurement of the opacity or density of the resulting image in adensitometer. From the data thus obtained, various photographiccharacteristics of the material can be determined. Thus, by plottingdensity against log exposure, a curve is obtained showing the gradationand sensitivity of the emulsion coating. Such tests are relatively timeconsuming, requiring hours or even days, and in the meantime,substantial portions of equipment are required to store the batch ofemulsion, contributing substantially to overhead costs.

It is an object of this invention to provide a rapid and simple methodfor determining relative densities produced upon exposure anddevelopment of a photographic emulsion, and hence, such properties asthe relative speed and contrast characteristics of the resultingsensitized material, with a high degree of accuracy,

said. method requiring relatively simple and economical equipment whichcan be readily operated without unusual skill, and which is adaptablefor a wide range of conditions of use.

We have discovered that samples of photographic emulsions of the typeemployed in making light sensitive layers by coating and dryingprocesses, particularly emulsions containing a? light-sensitive silverhalide such as silver bromide suspended in an aqueous gel formingcolloid such as aqueous gelatin, exposed in liquid form to light, andreduced in a standardized manner with a photographic developer, aredarkened to an extent which canbe accurately measured by determining theoptical density of a layer of standard thickness ofithe developedsample; and that these measurements bear substantially the sameinter-relationship as measurements obtained in the customary manner,described above, wherein a sample of the emulsion is coated on a sheet,dried, and test strips prepared therefrom by conventional exposure anddevelopment, and density measurements made from the test strips.

Thus, in accordance with one embodiment of the invention, comparativespeed and gradation obtainable in coated materials prepared with a batchof silver halide-gelatin emulsion are determined as follows: a sample ofthe liquid emulsion, as such, or if desired, diluted with apredetermined proportion of water, is divided into equal portions whichare placed in a number of containers of standard shape and size, whichare transparent to light of the type which it is desired to test forexposure of the emulsion. The samples are then irradiated respectivelywith graduated amounts of light, e. g., by using constant intensity anddiiferent periods of exposure, or a fixed period with illumination ofgraded intensity. A measured quantity of developer solution is thenadded to each of the irradiated samples, and after development for apredetermined period, the action is arrested by addition of a measuredquantity of a short stop or fixing solution. Thereupon, the density ofthe resulting coloration ,or opacity of the samples to transmitted lightis measured by conventional densitometer means. A curve or series ofcurves in which density is plotted against log exposure, obtained fromthe results of measurements made in this process, We have found,accurately represent the relative characteristics of the emulsion in thesame way as a curve or curves obtained by the conventional testingmethod. However, instead of requiring hours or days, the measurements inthe test of this invention are completed in a matter of minutes, thuspermitting further processing and use of the emulsion withoutsubstantial delay, and appreciably reducing the overhead expenseinvolved.

A convenient method of carrying out the testing procedure of thisinvention involves placing a series of samples of an emulsion on amoving belt or conveyor, and advancing the samples progressively tosuccessive stations at which dilution (if employed), exposure,development, addition of fixing or short stop solution, and measurementof density are respectively carried out. If desired, these operationscan be made automatically, or they can be carried out by hand. Theemulsion samples are shielded from light during all operations, exceptfor the controlled irradiation, until development is complete.

Moreover, if it is desired to maintain continuous control of thesensitivity or gradation of an emulsion, the successive steps of thepresent test can be carried out in a stream of emulsion flowing at apredetermined rate in a tube or conduit, dilution, exposure,development, fixing or short stop, and measurement of density takingplace by operations, or addition of reagents at a suitable rate, atsuccessive points in the flowing stream, measurement of density beingcarried out at a final point and the results of said measurement beingcontinuously recorded if desired.

The various steps in the process of the invention will be more fullyunderstood from the accompanying drawings which illustrate the procedureand the results obtained thereby. In the drawings,

Figure l is a schematic view showing a sample of emulsion in successivestages of the testing procedure.

Figure 2 similarly represents an arrangement for carrying out theprocedure of the invention in a continuous manner.

Figure 3 is a series of density-log exposure curves obtained in testinga typical silver bromide emulsion at various stages of ripening, inaccordance with the present invention.

Figure 4 is a series of curves prepared with the same emulsion as inFigure 3, in a parallel series of tests, employing the conventionalmethod of testing.

Referring to Figure 1, a quantity of photographic emulsion, e. g., asilver bromide-gelatin emulsion, is melted and thoroughly mixed withwater to form the test mixture [6. A dilution ratio can be chosen so asto yield a density or opacity, in the apparatus employed in the finalstep of the test hereinafter described, within the measuring range ofthe densitometer. For example, in testing one ordinary emulsion,dilution of 1 part by volume thereof with 30 parts by volume of waterwas found satisfactory. A

standard sample ll, e. g., about 20 cc. of the re- .1

obtained from light source H! and controlled by a suitable intensitycontrol device l5. The lat ter may include for example a neutral densitywedge for controlling intensity, an iris diaphragm, or the like. Theexposure is timed to yield the desired quantity of irradiation. Forexample, in the case of a silver bromide-gelatin emulsion of mediumsensitivity, an exposure of the order of two meter-candle-seconds issufficient to produce darkening. If it is desired to test thesensitivity of the emulsion to light of The cuvette may be onehavpredetermined spectral quality, an appropriate light source can beused for producing the desired wavelength, and if necessary, colorfilters can be interposed between the light source 14 and the cuvette i3containing sample H.

When exposure is complete, development is efiected by adding a measuredquantity (e. g., 5 cc.) of a developer solution iii to the sample II incuvette l3 and thoroughly agitating the resulting mixture. By employinga syringe I! for addition of the developer, sufficient force can beimparted to the stream of liquid to produce adequate mixing withoutadditional agitation. The developer is allowed to react with theirradiated sample for a predetermined period; for example, from 3 to 6minutes has been found satisfactory for a normal developer. Such adeveloper may contain, for example, the following ingredients insufiicient water to yield 1 liter of solution:

p-Methylamino phenol g 2 NazSOs g 100 Hydroquinone g 5 Borax g 2 Toarrest development at the end of the desired period, a reagent I8 isadded which may be, for example, 1 cc. of 2% acetic acid or 2 cc. ofacid fixing solution such as an aqueous solution containing 12% sodiumthiosulfate and 1% acetic acid.

The optical density of sample I I is then measured in a densitometer,shown as comprising a light source H, a collimator 2i] and aphotoelectric cell 2| receiving illumination from the collimator throughsample II, and registering the relative density of the latter on themeter 22.

A succession of cuvettes such as that shown in Figure 1 can be advancedin a series on a conveyor or belt, and the various operations describedabove can be carried out at successive stations along the belt, i. e.,automatically or by hand.

A difierent form of apparatus for the process of this invention is shownin Figure 2. In this case, the water for dilution and the melted silverhalide-gelatin emulsion are brought through conduits 23 and 24 into aproportioning device 25 in which they are thoroughly mixed and whereinthe relative amounts to yield the desired concentration are measured.

The diluted emulsion passes thence through a main flow tube 26 at aconstant predetermined rate of flow, and is subjected to uniformirradiation of desired intensity in an exposure zone 21, theillumination being derived from light source 28 and controlled by adevice 29 of the same type as the device l5 described hereinbefore.Beyond the exposure zone 21, a developer solution is introduced into theflowing stream at a constant rate maintained by a regulating, device 30,through a side tube 3| into the main flow tube 26.

Development occurs in the succeeding developing zone 32 which is made ofsufficient length and cross-section to afford the requisite period ofdevelopment for the flow rate of the stream.

To arrest development, a suitable solution such as dilute aoeticacid, oran acidified sodium thiosulfate solution, is introduced into the tube.2.6 through a side tube 33*joining the tube 26 at the end of developmentzone 32, the solution added at this point being introduced at a constantrate by means of the proportioning device 3 2. 1

Beyond the junction of inlet tube 33', tube 26 conducts thedeveloped'emulsion through a density measuring zone 35 in which a beamof light from a source 36 passes through collimator 31 and thencethrough the stream of emulsion in zone 35 to a photocell 38 of which theoutput controls a recording densitometer 39. A continver halide, and acorresponding correction should.

be made in order to determine absolute values for the sensitivitymeasurements.

Typical curves obtained in the procedure of Figure 1 are shown in Figure3. These curves were determined from a series of samples taken from thesame batch of silver bromide-gelatin emulsion at various intervalsduring the ripening period, and as indicated by the time in minutesshown in the drawing, the curves represent the density versus logexposure of the unripened emulsion and of the same emulsion afterripening for 5, 15, 35, 75, 95 and 115 minutes. For purposes ofcomparison, a parallel series of tests was made by coating sheets ofpaper with the same emulsion at the same time intervals during theripening treatment, drying, exposing to graded quantities ofillumination, measuring the resulting densities, and plotting theresults in terms of optical density versus log relative exposure. Theresulting curves are shown in Figure 4. A comparison of the two sets ofcurves clearly indicates that the slope and relative location of thecurves determined in accordance with the method of this invention yieldthe gradation and speed characteristics or inertia in the same .manneras curves obtained in the conventional testing procedure, and give thesame indication of completion of ripening.

Similar results have been obtained employing the procedures andapparatus hereinbefore described, but omitting the initial dilution ofthe emulsion sample with water. Instead, the emulsion, in liquid form,is introduced directly into the testing equipment, exposed in the formof measured samples or at a predetermined flow rate, in a layer ofsuitable standard depth to be translucent, to controlled quantities oflight; and after development in a standardized manner, as describedabove, the emulsion sample or samples are measured for density in alayer having a depth adapted to the range of the densitometer employed.In many cases, omission of the initial dilution step provides even moreaccurate or reliable results than when dilution is used.

The testing procedure of this invention can be applied to other types ofemulsions than silver bromide-gelatin emulsions, including thosecontaining other suspended light sensitive silver halides and viscouscolloidal suspension media other than aqueous gelatin, e. g., albumen,natural and artificial resins and gums, organic derivatives ofcellulose, and the like. When the suspension medium is not compatiblewith water, other solvents such as alcohol, acetone, or mixtures thereofwith water or with each other can be used for addition of developer,short-stop and fixing reagents, and for dilution, so as to preserve thecolloidal nature of the mixture during the test. Adidtional materialsmodifying the properties of the emulsions, such as sensitizingdyestuffs, color formers for color photography and the like can also bepresent in the emulsion during a test in accordance with the invention.

Emulsions for use in color photography can also be advantageously testedaccording to the process of this invention. Such emulsions contain, forexample, a color former which reacts with the oxidation products of thedeveloper, produced upon reaction with light-exposed silver halide, toform a dye. For example, the color formers can be naphthols, pyrazolonesor acylacetarylides yielding respectively cyan, magenta or yellow dyeswith oxidation products of a colorforming developer such asp-amino-diethylaniline. Emulsions containing a cyan color former aresensitized to red light, and those containing -a magenta color formerare sensitized to green,

while a yellow color former is generally employed with a color-blind orblue-sensitive silver halide emulsion.

In testing such emulsions in accordance with the present invention, thelight from source 14 or 28 of Fig. 1 or 2 for exposing the test emulsioncan be advantageously of the color to which the emulsion is sensitive,or in special cases, of another color for which it is desired to testthe sensitivity of the emulsion. The developer added at the next stageis chosen to yield a color with the color former. After addition of theshortstop, a reagent is added which converts the silver to silverhalide, e. g., a ferricyanide and sodium chloride solution. A fixingagent can also be added to dissolve the silver halide.- There is formedthereby a sample containing the developed color in a concentrationcorresponding to the sensitivity of the emulsion. The light from sourcei9 or 36 is chosen or filtered to have its principal wavelengthcorresponding to maximum I absorption of the color produced.Accordingly,

the intensity of illumination reaching the photocell 2| or 38 andindicated or recorded by meter 22 or 39 is a measurement of the colordensity produced in the emulsion, yielding data from whichsensitiometric curves can be plotted in the same manner as hereinabovedescribed.

The present testing procedure can be utilized to follow the ripening ofa batch of emulsion, to compare the speed and contrast of differentemulsions, to compare the development obtained under various conditionsof time, temperature, concentration and composition, and for other testswherein comparative densities were previously determined by making teststrips from the emulsion and developing and measuring the same in theconventional manner.

Variations and modifications can be made in this invention withoutdeparting from the scope or nature thereof, and portions thereof can beused without others.

We claim:

1. A process for measuring the sensitometric characteristics of a.photographic silver halide emulsion which comprises exposing a testportion of the emulsion in liquid form to a predeterniined quantity ofillumination, developing the e posed test portion while liquid, anddeterminin the optical density of the developed liquid test portion totransmitted light.

2. A process according to claim 1 wherein a predetermined proportion ofa diluent is added to the original emulsion to form said liquid testportion.

3. A process according to claim 1 wherein light of predeterminedspectral quality is employed in exposing said liquid test portion.

4a. A. process for measuring. gradation andspeed characteristics of aphotographic silver halide emulsion which comprises exposing. .a seriesof test portions of the emulsion in liquid form respectively to gradedquantities of illumination, developing the exposed test portions whileliquid: under similar conditions, and determining the optical densitiesof the developed. liquid test portions tov transmitted light.

5. A process for measuring the relative sensitometric characteristics ofan aqueous photographic silver halide emulsion Which comprises exposinga test portion of the emulsion in liquid form to a predeterminedquantity of illumination, developing the exposed test portion whileliquid, arresting development thereof at the end of a predeterminedperiod, and determining the optical density of the developed liquid testportion to transmitted light.

6. A process as defined in claim 5 wherein a fixing agent is added tothedeveloped liquid test portion prior to determination of the opticaldensity, so as to dissolve the silver halides therein.

7. A process for measuring the relative sensitometric characteristics ofa photographic silver halide emulsion which comprises placing a sampleof'the emulsion in liquid form in a transparent container, exposing thesample in the container to a predetermined quantity of illumination;adding a predetermined quantity of developer solution to the sample inthe container, and after a predetermined developing period, adding apredetermined quantity of short stop solution thereto, and measurin theopacity of the developed composition in the container to transmittedlight. 1

8. A process as defined in claim 7 wherein the short stop solutionincludes a fixing agent for dissolving the silver halides in the sample.

9. A continuous process for measuring the relative sensitometriccharacteristics of a photographic silver halide emulsion which comprisescausing a portion of the emulsion in liquid form to flowin. a stream ata predetermined constant rate, exposing a limited zone of said stream toillumination of predetermined intensity, adding a developer at aconstant rate to said stream beyond the exposure zone, adding adevelopment arresting reagent at a constant rate at a. point spaced fromthe point of introduction of said developer, the intervening portion ofthe stream constituting a development zone, and measuring the opticaldensity of the stream to transmitted light beyond said development zone.

10. A process for measuring the relative sensitometric characteristicsof a color-forming photographic silver halide emulsion which comprisesadjusting the concentration of a fluid sample of the emulsion to apredetermined value, exposing a test portion of the resultingcomposition in fluid form to a predetermined quantity of illuminationhaving a color to which the emulsion is sensitive, color-developing theexposed test portion and bleaching the silver thus produced, anddetermining the optical density of the developed test portion totransmitted light of a principal wavelength corresponding to maximumabsorption of thecolor produced in the test portion.

EDWARD ALLAN WILLIFORD MONROE HAMILTON SWEET.

REFERENCES CITED The following references are of record in. the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,126,516 Szasz Aug. 9, 19382,401,051 Grouse et a1. May 28, 1946 OTHER REFERENCES- Mees: Theory ofPhotographic Process, Mac- Millan (30., N. Y., 1946, page 593.

9. A CONTINUOUS PROCESS FOR MEASURING THE RELATIVE SENSITOMETRICCHARCTERISTICS OF A PHOTOGRAPHIC SILVER HALIDE EMULSION WHICH COMPRISESCAUSING A PORTION OF THE EMULSION IN LIQUID FORM TO FLOW IN A STREAM ATA PREDETERMINED CONSTANT RATE, EXPOSING A LIMITED ZONE OF SAID STREAM TOILLUMINATION OF PREDETERMINED INTENSITY, ADDING A DEVELOPER AT ACONSTANT RATE TO SAID STREAM BEYOND THE EXPOSURE ZONE, ADDING ADEVELOPMENT ARRESTING REAGENT AT A CONSTANT RATE AT A POINT SPACED FROMTHE POINT OF INTRODUCTION OF SAID DEVELOPER, THE INTERVENING PORTION OFTHE STREAM CONSTITUTING A DEVELOPMENT ZONE, AND MEASURING THE OPTICALDENSITY OF THE STREAM TO TRANSMITTED LIGHT BEYOND SAID DEVELOPMENT ZONE.